SCC investigation of low alloy ultra-high strength steel 30CrMnSiNi2A in 3.5wt% NaCl solution by slow strain rate technique

To evaluate stress corrosion cracking（SCC） mechanism of low alloy ultra-high strength steel 30CrMnSiNi2 A in environment containing NaCl, SCC behavior of the steel in 3.5wt% NaCl solution is investigated by slow strain rate technique（SSRT） with various strain rates and applied potentials, surface analysis technique, and electrochemical measurements. SCC susceptibility of the steel increases rapidly with strain rate decreasing from 1 · 10 5s 1to 5 · 10 7s 1, and becomes stable when strain rate is lower than 5 · 10 7s 1. SCC propagation of the steel in the solution at open circuit potential（OCP） needs sufficient hydrogen which is supplied at a certain strain rate.Fracture surface at OCP has similar characteristics with that at cathodic polarization 1000 mVSCE, which presents characteristic fractography of hydrogen induced cracking（HIC）.All of these indicate that SCC behavior of the steel in the solution at OCP is mainly controlled by HIC rather than anodic dissolution（AD）.

SCC evaluation of ultra-high strength steel in acidic chloride solution

The stress corrosion crack （SCC） susceptibility of ultra-high strength steel AerMet 100 was investigated by slow strain rate technique （SSRT）, tensile with polarization and surface analysis technique. The curves of tf^Cl/tf^W -strain rate are divided into three regions： stress-dominated region, SCC-dominated region, and corrosion-dominated region, so as the curves of εf^Cl/εf^W - strain rate and tm/tf-strain rate. The results of tensile tests with polarization show that the main SCC mechanism of AerMet 100 is anodic dissolution, which controls the corrosion process. The three regions have been discussed according to the relationship between the rate of slip-step formation and the rate of dissolution. Fracture appearances in different environments were analyzed by scanning electron microscopy （SEM）. SCC fracture appears as a mixture of intergranular and dimples, while it is totally dimples in the inert environment. The εf becomes the parameter to predict tf because the relationship between εf^Cl/εf^W and tf^Cl/tf^w is a straight line for AerMet 100.

Effects of Niobium and Vanadium on Hydrogen-Induced Delayed Fracture in High Strength Spring Steel

Influence of vanadium and/or niobium additions on delayed fracture behavior in high strength spring steel was studied by hydrogen permeation method and slow strain rate technique （8SRT）, and its mechanism was analyzed. The results show that apparent diffusion coefficient of hydrogen in microalloyed spring steels Nb-V-steel and Nb-steel is lower than that in non-microalloyed steel 60Si2MnA. Percentage of strength reduction in SSRT in air after precharged hydrogen of the microalloyed steels is smaller than that of 60Si2MnA. Addition of the microalloys changes the fracture characteristics. Thence, vanadium and/or niobium additions are a very effective and economy means to improve the hydrogen-induced delayed fracture resistance of high strength spring steel.